1. Field of the Invention
The present invention relates to large scale multi-hop wireless ad-hoc networks. It proposes a multicast routing algorithm for large scale wireless mesh networks.
2. Description of the Related Art
Wireless communication networks, such as mobile wireless telephone networks, have become increasingly prevalent over the past decade. These wireless communications networks are commonly referred to as “cellular networks”, because the network infrastructure is arranged to divide the service area into a plurality of regions called “cells”. A terrestrial cellular network includes a plurality of interconnected base stations, or base nodes, that are distributed geographically at designated locations throughout the service area. Each base node includes one or more transceivers that are capable of transmitting and receiving electromagnetic signals, such as radio frequency (RF) communications signals, to and from mobile user nodes, such as wireless telephones, located within the coverage area. The communications signals include, for example, voice data that has been modulated according to a desired modulation technique and transmitted as data packets. As can be appreciated by one skilled in the art, network nodes transmit and receive data packet communications in a multiplexed format, such as time-division multiple access (TDMA) format, code-division multiple access (CDMA) format, or frequency-division multiple access (FDMA) format, which enables a single transceiver at a first node to communicate simultaneously with several other nodes in its coverage area.
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed. In this type of network, each mobile node is capable of operating as a base station or router for the other mobile nodes, thus eliminating the need for a fixed infrastructure of base stations.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and thus communicate with nodes of other networks, such as those on the public switched telephone network (PSTN) and on other networks such as the Internet. Details of these advanced types of ad-hoc networks are described in U.S. Pat. No. 7,072,650 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, issued on Jul. 4, 2006, in U.S. Pat. No. 6,807,165 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, and in U.S. Pat. No. 6,873,839 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, issued on Mar. 29, 2005, the entire content of each being incorporated herein by reference.
The capacity of pure multi-hop wireless Ad Hoc networks diminishes as the number of nodes increases in the network as explained by P. Gupta and P. R. Kumar, in “The Capacity of Wireless Networks”, IEEE Transactions on Information Theory, Issue 2, March 2000, the entire content being incorporated herein by reference. In order to increase the capacity of multi-hop wireless Ad Hoc networks, fixed infrastructure nodes may be introduced into the network, as described in “The Capacity of Wireless Networks”, IEEE Transactions on Information Theory, Issue 2, March 2000, by P. Gupta and P. R. Kumar, and in “A Hybrid Network Implementation to Extend Infrastructure Reach,” Technical Report, January 2003, by M. J. Miller, W. D. List, and N. H. Vaidya, the entire content being incorporated herein by reference. In order to reduce the route discovery latency in this kind of hybrid multi-hop wireless Ad Hoc network, hybrid routing protocol and network management have been proposed in “A Hybrid Network Implementation to Extend Infrastructure Reach,” Technical Report, January 2003, and in U.S. Patent Application Pub. No. 2004/0143842A1, the entire content being incorporated herein by reference.
The essence of hybrid routing and network management protocols is, for each device in the network, to maintain a route to the access point (AP) proactively and discover other routes reactively. During the network operation, each device periodically refreshes the route and registration to the AP. This process actually maintains a spanning tree rooted at the AP. In order to support multicasting in the hybrid multi-hop wireless Ad Hoc networks, a multicast algorithm is needed. A number of multicast algorithms for wired networks were designed in recent decades. Protocol independent multicast—sparse mode (PIM-SM) as described in “PIM-SM: Protocol Specification”, RFC 2362, by D. Estrin et al., and core based tree (CBT) as described in “Core Based Trees (CBT) Multicast Routing Architecture”, RFC 2201, by T. Ballardie, both build shared trees among the group members to support multicast in large scale static networks. Protocol independent multicast—dense mode (PIM-DM) as described in “PIM v2 DM Specification”, Internet Draft, by S. Deering, distance vector multicast routing protocol (DVMRP) as described in “Distance Vector Multicast Routing Protocol”, RFC 1075, by D. Waitzman et al, and multicast open shortest path first (MOSPF) as described in “Multicast Extensions to OSPF”, RFC 1584, by J. Moy, all build source specific trees between sources and group members to support multicast in small scale static networks. None of these methods takes the high dynamics into consideration for the mobile networks. They are not suitable for infrastructure based large scale wireless mesh networks.
Multiple multicast algorithms for pure wireless ad hoc networks were proposed in the last few years. The tree-based multicast algorithms for wireless Ad Hoc networks include Multicast Ad-hoc On-demand Distance Vector (MAODV) protocol which is described in “Multicast Operation of the Ad-Hoc On-Demand Distance Vector Routing Protocol”, MobiCom'99, August 1999, by E. M. Royer and C. E. Perkins. MAODV dynamically builds a tree rooted at the multicast group leader. The mesh-based multicast algorithms include On-Demand Multicast Routing Protocol (ODMRP) which is described in “On-Demand Multicast Routing Protocol in Multihop Wireless Mobile Networks”, Mobile Networks and Applications, Volume 7, Issue 6, December 2002, by S. Lee, W. Su and M. Gerla. ODMRP dynamically establishes and maintains a mesh by the source on demand. Both algorithms can not support large dense wireless ad hoc networks with high dynamics due to the high latency of building the multicast routes and high routing overhead for large scale wireless networks. The meshed tree-based multicast algorithm Core Assisted Mesh Protocol (CAMP), which is described in US patent application US2001/0034793 A1, Oct. 25, 2001, uses multiple cores to mesh the shared tree to connect all the group members. However, its cores are dynamically elected, hence it cannot build the meshed tree in a very short time to support the fast topology change. Additionally, the cores are meshed to each other through the mobile nodes in the network, hence the meshing among cores are vulnerable to the mobility. Thus, none of the existing ad hoc multicast routings are suitable for the large scale mesh networks with high dynamics.
The proposed Multicast Mesh Scalable Routing (MMSR) deals with multicast support in the large scale wireless mesh networks with high dynamics.
Multicasting is a more efficient method of supporting group communication than unicasting or broadcasting, as it allows transmission and routing of packets to multiple destinations using fewer network resources. Along with widespread deployment of wireless networks, the fast-improving capabilities of mobile devices, and an increasingly sophisticated mobile work force worldwide, content and service providers are increasingly interested in supporting multicast communications over wireless networks. As more and more applications and network control protocols requiring the multicast support, multicast routing algorithms are necessary in wireless multi-hop ad-hoc networks to support high efficiency of the traffic distribution in multiple users in the network. Compared to other existing multicast routing algorithms for wireless networks, the proposed algorithm has better scalability for large scale, highly dynamic wireless ad-hoc networks with relatively low network overhead.